During the 1950's, fat products were produced by substituting, in effect, acetic acid for a portion of the fatty acids occurring in ordinary fats and oils so as to obtain predominantly either monoaceto or diaceto triglycerides or combinations of these (Feuge, R. O., Food Technology 9: 314-318 (1955)), or mixtures of these triglycerides with mono- or diaceto diglycerides. The fats were called acetoglycerides, and most of the publications (from two groups of investigators working independently) described acetostearins (ibid.).
Acetostearins are waxy fats having sharp melting points, which has limited their application in food products requiring more plastic or liquid fats. One study described the fats as "highly flexible" and elastic; at a temperature of 22.degree. C., they could be stretched more than 800% (Feuge, R. O., et al., J. Amer. Oil Chem. Soc. 29: 11-14 (1952)). When chewed in the mouth, diacetostearin has been described as "somewhat like a gum" (U.S. Pat. No. 2,615,160 to Baur, column 7, line 55). In contrast to fats bearing medium and/or long substituents, acetostearins also exhibit unusual polymorphism (Baur, F. J., J. Amer. Oil Chem. Soc. 31: 147-151 and 196-199 (1954) and the Feuge Food Technology paper cited above).
Because of the waxy, rubbery functional properties of the fats, they were suggested for use in candy, as well as in icings and frostings, in spray oils for crackers, in edible "beeswax" for synthetic honey, in chewing gum, and in protective coatings for products such as fruits, cheese, preserves, and meats (U.S. Pat. No. 2,615,160, column 7, lines 59 to 64). But in the intervening decades, waxy acetoglycerides have been primarily used as protective coatings, thin films, moisture barriers and plasticizers. The protective coatings are sometimes called "hot melts" and may contain antibiotics (U.S. Pat. No. 3,192,057 to Hines and Shirk) or polymeric materials (U.S. Pat. No. 3,388,085 to Levkoff and Phillips) to prolong the life of the coating.
Recent research in this laboratory has shown that acetoglyceride-type fats bearing long (C.sub.16 to C.sub.24), saturated pendant groups and short groups such as acetyl as well as propionyl and butyryl are low in calories, and their functional properties can De modified for a variety of edible uses (U.S. application Ser. No. 07/804,140, now U.S. Pat. No. 5,258,197 issued Nov. 2, 1993, cited above). Therefore, it would be desirable to have new and improved processes for making these types of fats.
The Feuge, et al., group of investigators at the Southern Regional Research Laboratory prepared acetostearins by acetylating stearins with acetic anhydride (Feuge, R.O., et al., J. Amer. Oil Chem. Soc. 29: 11-14 (1952)). Other acetoglycerides were prepared by converting starting material fats to mono- and diglycerides, generally by mixing them with glycerol and sodium hydroxide for 0.3 to 3 hours at 200.degree. to 250.degree. C. (Food Technology, cited above, at page 314, column 2, paragraph 1). The resulting technical grade mixture is then acetylated directly or purified and acetylated. To obtain a homogeneous reaction product for later acetylation, in some cases the glycerol reaction was conducted in the presence of phenol or cresol (Feuge, R. O., and Bailey, A. E., Oil and Soap 23: 259-264 (1946)). Difficulty was experienced in freeing the product of solvent without decomposition of the glycerides (ibid.).
Although acetylation of stearins with acetyl chlorides in chloroform in the presence of pyridine was employed to make acetostearin isomers (U.S. Pat. No. 2,615,159 to Jackson, column 2, lines 1 to 4), the Baur group generally employed an interesterification reaction to obtain acetostearin mixtures (U.S. Pat. No. 2,615,160). Triacetin was reacted with a conventional fat in the presence of a low temperature rearrangement catalyst such as sodium alkoxide suspended in xylene or other low-boiling hydrocarbon which is miscible with the fats (id., column 2, lines 22 to 32 and column 3, lines 8 to 10). Thus, the system used had two phases.
Reaction temperatures were fairly low because higher ones impaired catalyst activity (id., column 3, lines 26 to 28). The level of catalyst used at these temperatures had to be relatively high, and the amount had to be increased where less well processed feedstocks that poisoned the catalyst were employed. High shear during mixing of the reaction was also necessary to emulsify the two nonmiscible phases. The ratios of triacetin to fat employed were low (35:100 to 50:100 in the examples, columns 5 to 6), which limited the variety of acetoglycerides obtained with the method. Unreacted triacetin was removed by water washing so that a large percentage of triacetin was washed out with the waste water. Products were purified by distillation.
It would be desirable to have a process for preparing acetoglyceride fats for edible use that was free of potentially toxic or noxious solvents, and that eliminated the need for costly purification steps. It would also be desirable to have an efficient, economical process that minimized catalyst use and losses of starting materials.